1. Field of the Invention
This invention relates to zoom lenses and more particularly to zoom lenses of reduced total length.
2. Description of the Prior Art
Zoom lenses are very efficient because just one lens can satisfy the need for a great many focal lengths. However, today's zoom lenses generally have too long a total length, and inconvenience photographers using them on cameras. Various attempts have been made to shorten the total length of the zoom lens, for example, (1) by creating a new zoom type that facilitates reduction of the total length; (2) by increasing the refractive power of each unit of the zoom section; and (3) by shortening the total length of the relay system.
The first solution, creation of a new, shorter zoom type, is highly desirable, but still in the developmental stages. The second method is easy to use. However, as the power increases, the required tolerance for the axial misalignment between the moving lens units becomes critical and severe and is thus incompatible with mass production techniques. The third method, when employed in the zoom lens constructed with four lens units having positive, negative, positive and positive powers respectively, from front to rear, utilizes a fourth lens unit or relay system having a front component of positive power and a rear component of negative power. This is the so-called tele type. The shortest value for the distance from the front vertex of the relay system to the focal plane of the entire system heretofor possible with the use of the tele type is as long as 0.8, measured as the ratio of that distance to the focal length of the relay system. Hitherto, there has been no method to achieve a further reduction except to strengthen the refractive power of each of the front positive and rear negative components while sacrificing good balance of the various corrected aberrations.